Asphalt-based roof sheeting is typically used as a single ply roofing membrane for industrial and commercial flat roofs. These membrane systems are preferred over conventional "built-up" asphalt roofing because the membrane systems are easier and safer to install. Typically, the membrane is applied to the roof in long strips and the strips are joined to each other and to the substrate, usually by heating with a torch, so as to create a continuous roofing surface. The roofing element acts as its own hot melt adhesive.
Elasticity and flexibility facilitate processing, installation and most importantly overall use of the asphalt membrane. It is well known in the art to add synthetic or natural polymeric material to the asphalt-based membrane, thereby achieving elasticity and flexibility. Typically, vinyl and olefin polymers are added to accomplish such results. Asphalt-based materials containing such polymeric material will be referred to herein as "modified asphalt materials" or similar language.
Flame retardancy is also a desirable characteristic to impart to such membranes. Asphalt compositions containing polyolefins or vinyl copolymers, however, are not flame retardant. To impart flame retardancy, it is known to add halogenated olefinic elastomers, fillers such as antimony trioxide, decabromo diphenyl oxide, chlorinated alicyclic hydrocarbon, alumina trihydrate, and chlorinated or brominated paraffins, as is discussed in U.S. Pat. Nos. 4,839,412 and 4,851,463. More specifically, others have attempted to impart flame retardancy to asphalt compositions containing vinyl copolymers by the addition of monoammonium phosphate, ammonium sulfate and methyl hydrogen polysiloxane as in U.S. Pat. No. 4,804,696; by the addition of potassium citrate and methyl hydrogen polysiloxane as in U.S. Pat. No. 5,026,747; by the addition of brominated diphenyl ether, antimony oxide and zinc borate as in U.S. Pat. No. 5,100,715; by the addition of ammonium sulfate, methyl hydrogen polysiloxane, muscovite mica and magnesium silicate as in U.S. Pat. No.5,102,463; by the addition of colemanite as in U.S. Pat. No. 5,110,674; and by the addition of at least one halogenated flame retardant and at least one inorganic phosphorus containing compound as in U.S. Pat. No. 4,659,381.
A problem, however, arises when certain flame retardant additives are added to modified asphalt compounds. Particularly, the addition of calcium borate to an asphalt composition containing vinyl copolymers increases the viscosity of the resulting modified asphalt membrane. Increasing the viscosity of the membrane leads to several problems, namely, it decreases the processing speed at which the membranes are produced, it hinders the adjoining of the membrane seams once on the roof and, it shortens the useful life of the membrane. The membrane becomes brittle, specifically at cold temperatures.
A useful fire retardant membrane material should disperse or meltblend efficiently during processing, without such problems as foaming, evolution of toxic health and/or environmentally hazardous by-products, or the like.
A need exists therefore, for a modified-asphaltic material useful for the formation of a roofing membrane or the like, which material is easily processed substantially without hazardous by-products. The material should have good flame and smoke resistance, yet should retain adhesion to itself and to a substrate to which it might be applied, such as by the application of heat thereto. It is desirable that the material substantially retain the processing and use performance characteristics of the modified asphalt material without the addition of flame retarding components. The material and products according to the present invention meet these needs, as will be explored hereinbelow.